Question

Read the line from Hamlet cited in Shakespeare: The World as Stage. Barnardo: Who's there? What does this line most likely show about the setting of the scene? It takes place in a foreign land because Barnardo does not know everyone. It is dark because Barnardo has trouble seeing the other guard. It takes place in a castle because Barnardo is a guard. It is early in the morning because Barnardo arrives first on the scene.

Answer 1

The line "Who's there?" by Barnardo, in my opinion shows about the setting of the scene that It is dark because Barnardo has trouble seeing the other guard.
It is actually midnight, and Barnardo has come to be the guard for the night, because Francisco's shift has ended. 

Answer 2

It is dark because Barnardo has trouble seeing the other guard.

This scene takes place at midnight and it is so dark Barnardo cannot see the other guard. Barnardo shows up for his shift, but he can't clearly make out who Francisco is. Francisco has the same problem because instead of answering Barnardo he tells him to identify himself first. They get it figured out and Barnardo begins his shift.